Terminal distribution control for point-to-multipoint service in wireless communication system

ABSTRACT

A method for controlling a user equipment (UE) capable of receiving a point-to-multipoint service in a wireless communication system comprises receiving a point-to-multipoint service and performing a cell reselection in response to completion of the receiving of the point-to-multipoint service. The cell reselection is performed among multiple frequencies. The cell reselection may be performed in response to signaling from the network. The cell reselection may be performed regardless of whether cell reselection criteria are satisfied. The cell reselection criteria may comprise at least one of a cell reselection reference value between frequencies and a cell reselection reference value within a frequency. The cell reselection criteria may be embodied in frequency layer dispersion (FLD) information. Alternatively, the cell reselection criteria may be embodied in frequency layer convergence (FLC) information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/208,093 filed on Aug. 19, 2005 (now U.S. Pat. No. 7,953,034), whichpursuant to 35 U.S.C. §119(a) and (e), claims the benefit of earlierfiling date and right of priority to Provisional Application No.60/603,373, filed on Aug. 19, 2004 and Korean Application No.2005-0017866, filed on Mar. 3, 2005, the contents of which are herebyincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to point-to-multipoint servicein a wireless communication system and, more particularly, to terminaldistribution control for point-to-multipoint service.

BACKGROUND OF THE INVENTION

The UMTS (universal mobile telecommunications system) is a thirdgeneration mobile communications system evolved from the European GSM(Global System for Mobile Communications) system and aims to provideimproved mobile communication services based on a GSM core network and awideband code division multiple access (W-CDMA) technology.

FIG. 1 is a block diagram illustrating a structure of a UMTS network.

Referring to FIG. 1, the UMTS system generally consists of a terminal(e.g., user equipment (UE)), a UTRAN (UTMS radio access network) and aCN (core network). The UTRAN includes one or more RNSs (radio networksub-systems). Each RNS includes a single RNC (radio network controller)and one or more base stations (e.g., node-Bs) managed by the RNC. EachNode B managed by the RNC receives information sent from a physicallayer of a terminal on the uplink, and transmits data to the terminal onthe downlink. Thus, the node-B serves as an access point to the UTRANfor the terminal. The RNC allocates and manages radio resources, andserves as an access point to the CN for the UTRAN.

FIG. 2 is a diagram illustrating a connection structure between a UTRANand a terminal in a UMTS network. As such, FIG. 2 shows an exemplaryarchitecture of radio interface protocols between a terminal and a UTRANbased on a 3GPP radio access network specification.

Referring to FIG. 2, the radio protocol is horizontally arranged toinclude a physical layer, a data link layer and a network layer. Theradio protocol is vertically divided into a user plane for transmittingdata information and a control plane for transferring control signals.Furthermore, the protocol layers shown in FIG. 2 may be divided into afirst layer L1, a second layer L2 and a third layer L3, based upon thethree lower layers of an open system interconnection (OSI) specificationmodel that is well-known in the art of communications systems.

The first layer L1 (e.g., the physical layer) uses physical channels toprovide information transfer service to its upper layers. The physicallayer is connected via a transport channel to a medium access control(MAC) layer located at an upper layer thereof. Data between the mediumaccess control layer and the physical layer is transferred via thistransport channel. Furthermore, the data between different physicallayers, i.e. between physical layers of transmitting side and receivingside, is transferred via the physical layer.

The MAC layer of the second layer L2 provides services to an upper radiolink control (RLC) layer via a logical channel. The RLC layer of the L2supports reliable data transmissions and performs segmentation andconcatenation of RLC SDUs (service data units).

The RRC (Radio Resource Control) layer positioned in the lowest portionof the third layer (L3) is defined in the control plane and controls thetransport channels and the physical channels for establishment,reconfiguration, and release of radio bearers (RBs). The RB indicates aservice by the L2 for a data transfer between the terminal and theUTRAN. In general, establishing the RB denotes processes of stipulatingthe characteristics of a protocol layer and a channel, which arerequired for providing a specific service, and setting correspondingparameters and operation methods.

When the RRC layer of a specific terminal and the RRC layer of the UTRANare connected to each other to exchange RRC messages, the correspondingterminal is in a RRC connected state. On the contrary, when notconnected to each other, the corresponding terminal is in an idle state.The terminal in the RRC connected state is further divided into URA_PCHstate and CELL_PCH state, CELL_FACH state and CELL_DCH state. Terminalsin the idle state or the URA_PCH state and CELL_PCH state use adiscontinuous reception (DRX) method to reduce power consumption,thereby discontinuously receiving a physical channel (i.e., SCCPCH(secondary common control physical channel)) to which a physical channel(i.e., PICH (paging indicator channel)) and a transport channel (i.e.,PCH (paging channel)) are mapped. The terminal is in a sleeping modeduring the remaining time periods excluding those times when receivingthe PICH or the SCCPCH. The terminal performing the DRX method wakes uponce per DRX cycle length to receive a PI (paging indicator) of the PICHchannel.

The terminal in the RRC connected state may further have a signalingconnection with the CN. In this case, the signaling connection indicatesa path for exchanging control messages between the terminal and the CN.The RRC connected state denotes a connection between the terminal theUTRAN, while the signaling connection denotes a connection between theterminal and the CN. The terminal uses the signaling connection toinform the CN of its position and/or to request services. The terminalshould be in the RRC connected state to have a signaling connection.

A MBMS (multimedia broadcast/multicast service) is described below.

The MBMS refers to a service for providing streaming or backgroundservices to a plurality of terminals using a downlink dedicated MBMSbearer service. In the UTRAN, the MBMS bearer uses a point-to-multipointradio bearer (RB) and a point-to-point RB. At this time, thepoint-to-multipoint RB uses a common channel (e.g., using the SCCPCH asa physical layer) so that a plurality of terminals subscribed to acorresponding service may receive the service.

The MBMS is divided into a broadcast mode and a multicast mode. The MBMSbroadcast mode is a service for transmitting multimedia data to allusers within a broadcast area. Conversely, the MBMS multicast mode is aservice for transmitting the multimedia data only to a specific usergroup within a multicast area. The broadcast area refers to a region inwhich it is possible to transmit the broadcast service, and themulticast area refers to a region in which it is possible to transmitthe multicast service.

FIG. 3 is a diagram illustrating an example of the UMTS networkproviding a point-to-multipoint service to the terminal.

Referring to FIG. 3, a UE1 performs a subscribing process in order toreceive an MBMS service. The UE1 also receives a service announcementprovided by the network regarding the MBMS service. Subscribing refersto the establishment of a relationship between a service provider and auser. A service announcement refers to providing the terminal an indexand other information related to the services to be provided. Forexample, a terminal that desires to receive the MBMS service of amulticast mode should join a multicast group. The multicast group refersto a group of terminals receiving a specific multicast service. Joiningrefers to a user merging with other users in a multicast group toreceive a particular multicast service. The terminal may inform the UMTSnetwork that it desires to receive specific multicast data through MBMSmulticast joining. On the contrary, leaving is a procedure in which aterminal that joined a specific multicast group releases its joining tothe multicast group. Each terminal performs such subscribing, joiningand leaving processes. The terminal may perform the subscribing,joining, and leaving processes any time of before, during, or after datatransmission.

During performance of a specific MBMS service, one or more sessions maysequentially be generated with respect to the MBMS service. If data tobe transmitted for the specific MBMS service is generated in a MBMSservice source, the CN notifies a session start to the RNC. However, ifthere is no data to be transmitted for the specific MBMS service in theMBMS service source, the CN notifies a session end to the RNC. The datatransmission with respect to the specific MBMS service may be carriedout between the session start and the session end. At this time, thedata transmitted through the data transmission process is transmittedonly to terminals that have joined the multicast group.

In the session start process, the UTRAN receives the session startnotification from the CN and transfers a MBMS notification to theterminals. The MBMS notification refers to the UTRAN informing aterminal that the data transmission of the specific MBMS service in acell is imminent. The MBMS notification may be transmitted multipletimes before the transmission of the data pertaining to the service.When carrying out the MBMS notification process, the UTRAN may alsocount the number of terminals receiving the specific MBMS service withina cell. The counting may be used for determining whether apoint-to-multipoint RB or a point-to-point RB is set as the RB fortransmitting the specific MBMS service data, or whether no RB is set.

The UTRAN internally establishes a threshold value to select anappropriate MBMS RB. After the UTRAN counts the number of terminals, ifthe counted number of terminals receiving the corresponding MBMS servicewithin the corresponding cell is smaller than the threshold value, theUTRAN establishes a point-to-point RB. However, a point-to-multipoint RBis established if the counted number of terminals is greater than thethreshold value. After determining the MBMS RB, the UTRAN informs theterminals of the establishment information of the corresponding RB.

When the point-to-point RB is established for the specific service, theterminals that desire to receive the service must be in the RRCconnected mode state. However, when the point-to-multipoint RB isestablished for the specific service, the terminals that desire toreceive the service do not have to be in the RRC connected mode state.That is, terminals in an idle state may also receive the MBMS servicedata by using the point-to-multipoint RB. However, if no terminals arecounted, the UTRAN does not establish any RB and does not transmit theMBMS service data. As such, the UTRAN establishing an RB when there isno user who wants to receive the service may cause undesirableconsumption of radio resources. The UTRAN initiates a transmission forMBMS service data received from the CN during a session using thedetermined RB.

During the counting process, the UTRAN does not have any informationpertaining to terminals in an RRC idle mode. Accordingly, when theterminals in the RRC idle mode are requested by the UTRAN for counting(with respect to MBMS services subscribed by the terminals), theterminals in the RRC idle mode implement an RRC connection with theUTRAN. As a result, the terminals notify the UTRAN that the terminals inthe RRC idle mode want to receive the specific MBMS service.

However, when the terminals have a signaling connection with the SGSN(serving general packet radio service support node), the SGSN informsthe UTRAN of information related to the MBMS of the terminals. Theinformation includes a list of MBMS services subscribed to by theterminals. Therefore, the UTRAN may recognize whether the terminals havesubscribed to a specific MBMS service. Accordingly, the terminals do notrespond to the request for the counting from the UTRAN. Terminals whichdo not have the signaling connection with the SGSN but are in the RRCconnected state may inform the UTRAN of the list of MBMS servicessubscribed to by the terminals. Hence, the UTRAN may recognize thenumber of terminals desiring to receive the specific MBMS servicewithout receiving any response from the terminals in the RRC connectedstate.

The UTRAN may perform the counting process during a session of the MBMSservice or in the initial step of the MBMS service. This is because,during the MBMS session, the terminal may move into another cell, turnoff its power, or discontinue use of the MBMS service. Therefore, thenumber of terminals desiring to receive the MBMS service in a cell maychange. Thus, the UTRAN may perform the counting process to establishthe RB more efficiently even while the MBMS session is ongoing.

A FLC (Frequency Layer Convergence) is described below.

In the UMTS system, a base station may actually use one or morefrequency bandwidths. That is, because all users may not receiveservices with appropriate qualities using only one frequency bandwidthin an area where many users are congregated (e.g., in a hot-spot),service providers consider the service demand in a region where the basestation is positioned in order to provide services by using more thanone frequency bandwidth.

When one base station uses several frequencies, for example severaladjacent frequencies, the propagation characteristics of radio waves ineach frequency have many similarities. If one MBMS service is providedusing a power level corresponding to approximately ten percent of theentire power available for a specific frequency in a specific cell, whenthe base station provides the same MBMS service at other frequencies,significant radio resources may be consumed.

Therefore, when a base station uses several frequencies, the basestation selects one frequency among the available frequencies to providethe MBMS service. The terminals then move to the selected frequency. Thepreceding operations are referred to as FLC (Frequency LayerConvergence). The specific frequency selected by the base station toprovide the MBMS service is referred to as a preferred frequency.

In FLC, when notifying terminals of a MBMS start, the base stationinforms the terminals of the preferred frequency on which the MBMSservice is provided to induce the terminals to move to the specificfrequency. To this end, the base station informs the terminalspositioned at frequencies other than the preferred frequency that theMBMS service is provided only at the preferred frequency. Then, theterminals carry out a cell reselection procedure. When a condition forchanging a cell is satisfied, the terminals reselect a cell to move tothe preferred frequency.

The cell reselection by the terminals is described below.

The cell reselection process is a process for positioning a terminal ina cell that provides services of at least a minimum quality. In thisprocess, the terminal compares the quality of a serving cell against thequality of a neighboring cell. If the quality of the neighboring cell issuperior to that of the serving cell, the terminal reestablishes theneighboring cell as its serving cell.

Cell quality may be influenced by radio wave environment, which maychange in an irregular manner. As a result, a terminal located at aboundary of more than two cells frequently performs cell reselection inan alternating fashion (e.g., selecting different cells in turn).Whenever cell reselection is performed, the terminal must re-registerits location with a new cell or temporarily stop data transmissions.Accordingly, cell reselection should not be performed more frequentlythan necessary, to prevent waste of resources. Accordingly, when thequality of the serving cell is higher than a specific reference value,the terminal does not perform cell reselection. The specific referencevalue is set at a value by which services may be provided at asatisfactory level to the terminal. That is, even if the serving celldoes not provide better quality than neighboring cells, if the qualityof the serving cell is higher than the specific reference, then theterminal does not perform cell reselection.

When a base station uses several frequencies, each frequency may be fora particular cell, and the cell reselection is used in Cell_PCH,Cell_FACH, URA_PCH and idle mode in which the UTRAN does not assign acell where the terminal should be positioned.

FLC is described in relationship with cell reselection, below. When afrequency in a cell in which a terminal is positioned is not a preferredfrequency, the terminal receives information regarding the preferredfrequency from a base station at an initial step of the MBMS service.However, as described above, if the quality of the cell in which theterminal is positioned exceeds a specific reference value, the terminaldoes not perform the cell reselection process. Because the MBMS servicesubscribed by the terminal is provided only at the preferred frequency,if the terminal does not move to the preferred frequency, the terminalmay not receive the service to which it subscribed. Therefore, in orderfor the terminal to receive the service to which it has subscribed, whena specific MBMS service is provided only at a preferred frequency andthe terminal does not position itself at the preferred frequency, theterminal performs the cell reselection process even if the quality ofthe serving cell where the terminal is positioned is higher than thespecific reference value.

In the cell reselection process, the base station informs the terminalof an offset value to facilitate the selection of the preferredfrequency by the terminal. The offset value is added to a qualitymeasurement value of a cell positioned at the preferred frequency or isexcluded from a quality measurement value of a cell not positioned atthe preferred frequency. A specific frequency or a specific cell isdetermined to have a quality better than that of other cells based onthis offset value. Accordingly, the base station may increase theprobability that the terminal moves to the preferred frequency or thespecific cell.

As mentioned above, the FLC is a method for positioning a plurality ofterminals at a specific frequency bandwidth in a certain area. That is,using this FLC method, the base station may reduce consumption of radioresources to provide the MBMS service to the terminals.

However, the FLC deliberately changes a distribution of terminals inorder to position many terminals at a preferred frequency. As a result,many terminals are positioned at the preferred frequency, but arelatively small number of terminals are positioned at otherfrequencies. Therefore, a load is converged only upon a specific cell,causing an imbalance between the frequencies and cells. In addition, ascompared to a uniform distribution of terminals over several cells, whenFLC is implemented, the terminals may receive services of lesserquality, resulting in an inefficient allocation of radio resources.

As described above, at the initial step of the MBMS service, theterminal performs the cell reselection process to move into the cell ofthe preferred frequency on the basis of information transmitted from thebase station even if the quality of the serving cell in which theterminal is positioned exceeds a certain reference value. However, aftercompleting the MBMS service, when the quality of the cell in which theterminal is positioned exceeds the specific reference value, theterminal does not move into a new cell but remains positioned at thepreferred frequency. That is, the state of the MBMS service start, i.e.that terminals positioned at other frequencies are converged upon thepreferred frequency, continues until after the MBMS service iscompleted. A problem may occur, however, in which the number ofterminals to which a cell may provide services with the appropriatequality is exceeded. This problem may continue even after the MBMSservice has ended.

In general, if the terminal is positioned in a cell with the bestquality, much data may be exchanged with the base station even withrelatively low power. However, depending on the current FLC method ofthe MBMS service, although the terminal may receive a service with farbetter quality from another frequency or cell after the MBMS service iscompleted, the terminal does not change the frequency. Instead, theterminal remains continuously positioned at the same frequency as longas the quality of the currently selected cell is higher than a certainreference value. This distribution of terminals after the MBMS serviceis completed may waste power in terminals.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to terminal distributioncontrol for point-to-multipoint service that substantially obviates oneor more problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide uniform distribution ofterminals that were converged upon a specific preferred frequency due toFLC (Frequency Layer Convergence), over several frequencies uponpoint-to-multipoint service completion.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, inone embodiment, a method for controlling a user equipment (UE) capableof receiving a point-to-multipoint service in a wireless communicationsystem comprises receiving a point-to-multipoint service and performinga cell reselection in response to completion of the receiving of thepoint-to-multipoint service. The cell reselection is performed amongmultiple frequencies.

The cell reselection may be performed in response to signaling from thenetwork. The cell reselection may be performed regardless of whethercell reselection criteria are satisfied. The cell reselection criteriamay comprise at least one of a cell reselection reference value betweenfrequencies and a cell reselection reference value within a frequency.

The cell reselection criteria may be embodied in frequency layerdispersion (FLD) information. Alternatively, the cell reselectioncriteria may be embodied in frequency layer convergence (FLC)information.

The point-to-multipoint service may be a multimedia service. Thepoint-to-multipoint service may be received from a UTMS terrestrialradio network (UTRAN). The cell reselection may be performed amongavailable frequencies.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings. It is to be understood that both the foregoinggeneral description and the following detailed description of thepresent invention are exemplary and explanatory and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block diagram illustrating a structure of a UMTS network.

FIG. 2 is a diagram illustrating a connection structure between a UTRANand a terminal in a UMTS network.

FIG. 3 is a diagram illustrating an example of the UMTS networkproviding a point-to-multipoint service to the terminal.

FIG. 4 is a diagram illustrating terminal distribution control for apoint-to-multipoint service, according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention may be embodied in a mobile communications systemsuch as the UMTS (Universal Mobile Telecommunications System) developedby the 3GPP. However, the present invention may also be applied tocommunications systems operated using other specifications. Furthermore,the point-to-multipoint service referred to herein may be a multimediabroadcast/multicast service (MBMS) or other type of service.Additionally, the terminal referred to herein may be a user equipment(UE) or other type of terminal.

Using the present invention, a UTRAN may utilize and share resourcesmore efficiently. Furthermore, a terminal may receive services in a cellmore efficiently and with better quality. In one embodiment, a terminalmoving into a preferred frequency by FLC (Frequency Layer Convergence)performs cell reselection and moves to a frequency with a relativelybetter quality, after a corresponding MBMS service is completed. Thatis, when the MBMS service is completed, the terminal is notified of thecompletion of the MBMS service by the base station and performs a cellreselection process. In the cell reselection process, the terminalsearches available frequencies as candidate frequencies. The completionof an MBMS service is also known as the end of an MBMS session.

Furthermore, when the MBMS service is completed, the base station mayuniformly distribute many terminals converged upon a preferred frequencyover several frequencies. The base station may recognize the loadgenerated in each cell at each frequency. Therefore, the base stationmay regulate FLC information to congregate multiple terminals on aspecific frequency bandwidth. The specific frequency bandwidth that themultiple terminals are converged upon by the base station is thepreferred frequency. Alternatively, the base station may instruct themultiple terminals to be distributed over several frequency bandwidths.

The FLC information may include details regarding the frequencies thateach MBMS is being transmitted. The FLC information may also includedetails regarding measuring parameters, measurement compensated values,or offsets to be applied to cells when the terminal performs cellreselection. Furthermore, the FLC information may include a basis fordetermining a cell change, or instructions regarding whether the cellreselection should be performed with respect to various frequencies.

When the base station provides the MBMS service, if the number ofterminals converged on the preferred frequency is not high enough tocause problems in providing other services, or if the terminals havealready been converged to maximum capacity on another frequency andadditional terminals may not be converged on the another frequency, thebase station does not instruct the terminals to perform cellreselection, even if the MBMS service is completed. However, when thebase station is required to distribute terminals converged on thepreferred frequency over several frequencies, the base station mayinstruct the terminal to perform cell reselection, even though thequality of a preferred frequency in a cell at which the terminal iscurrently positioned is greater than a cell reselection reference value.

FIG. 4 is a diagram illustrating terminal distribution control for apoint-to-multipoint service, according to an embodiment of the presentinvention.

Referring to FIG. 4, the base station transmits FLC information and theterminals move to the preferred frequency based on the FLC information.The terminals then receive the MBMS service. When the MBMS service iscompleted, the terminals may perform cell reselection by measuring thequalities of available frequencies and selecting a frequency in a cellhaving the best quality. The selected frequency may be in the currentserving cell or another cell. If the terminal selects a frequency inanother cell, the another cell is designated as the serving cell. Theselection of a new serving cell may occur regardless of whether thequality of the new serving cell is higher than the cell reselectionreference value. The cell reselection reference value may preferably bea cell reselection reference value between frequencies (Sintersearch) ora cell reselection reference value within a frequency (Sintrasearch).

After the MBMS session ends, the terminal may perform cell reselectionregardless of the cell reselection reference value until the terminalmeasures qualities of several frequencies in order to select a frequencyto be positioned. The terminal then moves to the selected frequency.Furthermore, cell reselection may be performed when the quality value ofthe serving cell is less than a specific reference value.

During reception of the MBMS service by the terminal, when FLCinformation (e.g., information regarding a preferred frequency) ischanged, when FLC information is not being transmitted from the basestation, or when the base station notifies the terminal that the FLC isnot being used, the terminal may perform cell reselection regardless ofthe cell reselection reference value with respect to availablefrequencies. Available frequencies are frequencies adjacent to theserving cell where the terminal is positioned.

Furthermore, in another embodiment, a plurality of frequencies may beestablished as the preferred frequency. In such case, service qualitymay be maintained despite convergence. To this end, the base station mayassign a plurality of frequencies as the preferred frequency and informthe terminal through a MCCH (MBMS Control Channel). Upon receiving thenotification from the base station that more than one frequency isassigned as the preferred frequency, the terminal adds an offset value,which may be provided by the base station, to the preferred frequency toperform cell reselection.

In cell reselection, if a plurality of preferred frequencies are relatedto a specific MBMS service transmitted from the base station, theterminal may select an arbitrary frequency and then select a cell thathas the arbitrary frequency bandwidth as its serving cell. Furthermore,if a plurality of preferred frequencies related to the specific MBMSservice are transmitted from the base station, the terminal may measurethe quality of the cell of the preferred frequency bandwidth to select afrequency bandwidth with an optimal quality and set the cell of thecorresponding frequency bandwidth as its serving cell.

Furthermore, in cell reselection, when the number of preferredfrequencies related to the specific MBMS service received from the basestation is changed, the terminal measures each frequency bandwidth toselect an arbitrary bandwidth and then moves to the correspondingfrequency bandwidth. Additionally, during cell reselection, when thenumber of preferred frequencies related to the specific MBMS servicereceived from the base station is changed, the terminal measures eachfrequency bandwidth to select a frequency bandwidth which provides thebest quality and then moves into the corresponding frequency bandwidth.Also, in the cell reselection process, when the FLC informationtransmitted from the base station to the terminal does not include theinformation related to the preferred frequency, the terminal performsthe cell reselection process by searching available frequencies ascandidate frequencies.

However, once the MBMS service is completed, when the cell reselectionprocess is required to search several frequencies as candidatefrequencies, measurement of the qualities with respect to availablefrequencies by the terminal in order to determine a cell to bepositioned may require a significant time period. This time period formeasurement may result in an increase in service disconnection time forthe terminal. Therefore, after the MBMS service is completed, when theterminal performs cell reselection by searching various frequencies ascandidate frequencies, the terminal may not measure all frequencies.Rather, the terminal may select an arbitrary frequency among theavailable frequencies, and move to the cell of the arbitrary frequency.

In one embodiment, a method for controlling a user equipment (UE)capable of receiving a point-to-multipoint service in a wirelesscommunication system comprises receiving a point-to-multipoint serviceand performing a cell reselection in response to completion of thereceiving of the point-to-multipoint service. The cell reselection isperformed among multiple frequencies.

The cell reselection may be performed in response to signaling from thenetwork. The cell reselection may be performed regardless of whethercell reselection criteria are satisfied. The cell reselection criteriamay comprise at least one of a cell reselection reference value betweenfrequencies and a cell reselection reference value within a frequency.

The cell reselection criteria may be embodied in frequency layerdispersion (FLD) information. Alternatively, the cell reselectioncriteria may be embodied in frequency layer convergence (FLC)information.

The point-to-multipoint service may be a multimedia service. Thepoint-to-multipoint service may be received from a UTMS terrestrialradio network (UTRAN). The cell reselection may be performed amongavailable frequencies.

The present invention may provide for, after an MBMS service iscompleted, the terminal may perform cell reselection. Accordingly, theterminal may move into a cell in which a service is provided with anoptimal quality. Therefore, load may be minimized from being convergedupon a specific cell.

It will be apparent to those skilled in the art that variousmodifications and variations may be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for controlling a user equipment (UE)configured to receive a point-to-multipoint service in a wirelesscommunication system, the method performed by the UE and comprising:receiving the point-to-multipoint service; completing the reception ofthe point-to-multipoint service by releasing a point-to-multipoint radiobearer; and performing a cell reselection based on control informationreceived from a base station after the completion of the reception ofthe point-to-multipoint service, wherein the control informationincludes a first parameter associated with measurement betweenfrequencies and a second parameter associated with measurement within afrequency, wherein performing the cell reselection comprises: selectinga frequency randomly from among a plurality of frequencies using thecontrol information; and selecting a suitable cell within the selectedfrequency, wherein the point-to-multipoint service is received based ona frequency indicated by the control information, wherein the cellreselection is performed when the UE decides to no longer receive thepoint-to-multipoint service, wherein the cell reselection is performedamong multiple frequencies without measuring all candidate frequencies,wherein the control information further includes frequency layerconvergence (FLC) information, wherein the FLC information indicates atleast one preferred frequency, wherein the FLC information includes anoffset to be applied to the at least one preferred frequency, andwherein the offset is added to a quality measurement value of a cellpositioned at the preferred frequency for comparing the cell withanother cell during the cell reselection.
 2. A user equipment (UE) forreceiving a point-to-multipoint service in a wireless communicationsystem, the UE comprising: means for receiving the point-to-multipointservice; means for completing the reception of the point-to-multipointservice by releasing a point-to-multipoint radio bearer; and means forperforming a cell reselection based on control information received froma base station after the completion of the reception of thepoint-to-multipoint service, wherein the control information includes afirst parameter associated with measurement between frequencies and asecond parameter associated with measurement within a frequency, whereinthe means for performing the cell reselection performs the cellreselection by: selecting a frequency randomly from among a plurality offrequencies using the control information; and selecting a suitable cellwithin the selected frequency, wherein the point-to-multipoint serviceis received based on a frequency indicated by the control information,wherein the cell reselection is performed when the UE decides to nolonger receive the point-to-multipoint service, wherein the cellreselection is performed among multiple frequencies without measuringall candidate frequencies, wherein the control information furtherincludes frequency layer convergence (FLC) information, wherein the FLCinformation indicates at least one preferred frequency, wherein the FLCinformation includes an offset to be applied to the at least onepreferred frequency, and wherein the offset is added to a qualitymeasurement value of a cell positioned at the preferred frequency forcomparing the cell with another cell during the cell reselection.
 3. Themethod of claim 1, wherein the cell reselection is performed if avariable related to previous frequency information for thepoint-to-multipoint service is not empty.
 4. The UE of claim 2, whereinthe cell reselection is performed if a variable related to previousfrequency information for the point-to-multipoint service is not empty.